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Zinc has been claimed to reduce cold symptoms, help infants recover from infectious diseases, slow progression of age-related macular degeneration, and help wound healing.

Zinc has been suggested to increase insulin sensitivity.

Mild zinc deficiency impairs growth in children and can be corrected with zinc supplementation (1, 2).

The US Food and Drug Administration (FDA) granted orphan drug designation to zinc acetate for treating Wilson disease to prevent dangerous copper level elevation.

A 2013 Cochrane review of 16 therapeutic trials (1387 participants) and 2 preventive trials (394 participants) demonstrated that zinc reduced the duration (in days) but not the severity of common cold symptoms (3). Although the proportion of participants with symptoms after 7 days of treatment was significantly smaller than those in the control groups, adverse effects, such as bad taste and nausea, were higher in the zinc group and should be taken into consideration (3). A 2017 meta-analysis reported no difference in efficacy between zinc acetate and zinc gluconate lozenges in treatment of colds and no evidence for greater efficacy of daily doses higher than 100 mg (4). Most studies have evaluated treatment rather than prevention of the common cold; however, a 2021 meta-analysis of 28 trials (5446 subjects) reported that, compared to placebo, zinc prevented 5 upper respiratory tract infections per 100 person months with a number needed to treat of 20 (5). The study reported that symptoms resolved 2 days earlier compared to placebo and more subjects were likely to remain symptomatic after 7 days without zinc.

There is strong evidence that, in developing countries, supplements containing zinc 20 mg and 20 mg iron taken once a week, when given for the first 12 months of life, reduce infant mortality due to diarrhea and respiratory infections (6). A 2016 Cochrane review found that zinc supplementation may be beneficial to treat diarrhea in zinc-deficient or malnourished children who are over 6 months old (7).

There is also strong evidence that supplements containing zinc 40 to 80 mg and antioxidants (vitamin C and E and lutein/zeaxanthin) taken once/day slow progression of moderate to severe atrophic (dry form) age-related macular degeneration (8-9).

Clinical data on zinc for treatment of diabetes are emerging. A 2019 systematic review and meta-analysis of 32 randomized placebo controlled trials (1700 subjects) using zinc monosupplements or with co-supplements in patients with prediabetes or diabetes, obesity or overweight, and pregnant women with prediabetes or diabetes, found a significant decrease in fasting glucose of 14 mg/dL (0.8 mmol/L) and hemoglobin A1C of 0.55% (10). However, the hemoglobin A1C reduction with zinc monosupplement treatment was only 0.35%.

Zinc is generally safe, but toxicity can develop if high doses are used (see page Toxicity). The common adverse effects of zinc lozenges include nausea, vomiting, diarrhea, mouth irritation, mouth sores, and bad taste.

Because zinc is a trace metal and can remove other necessary metals from the body, zinc lozenge dose should not exceed 75 mg per day (total dose, regardless of dosing frequency) for 14 days.

Zinc sprays may cause nose and throat irritation, and intranasal forms may result in anosmia.

The absorption and effect of certain antibiotics (eg, cephalexin, tetracyclines, quinolones) may be diminished by the oral zinc supplements; therefore, zinc should be taken at least 2 hours before or 4 to 6 hours after the antibiotic.

Zinc may stimulate tumor cell production of metallothionein, which may inactivate cisplatin, chelate integrase inhibitors (dolutegravir), and also decrease penicillamine levels by forming an insoluble complex.

1. 1. Mayo-Wilson E, Junior JA, Imdad A, et al: Zinc supplementation for preventing mortality, morbidity, and growth failure in children aged 6 months to 12 years of age. Cochrane Database Syst Rev, 5:CD009384, 2014. doi: 10.1002/14651858

2. 2. Lassi ZS, Kurji J, Oliveira CS: Zinc supplementation for the promotion of growth and prevention of infections in infants less than six months of age. Cochrane Database Syst Rev 4:CD010205, 2020. doi: 10.1002/14651858.CD010205.pub2

3. 3. Singh M, Das RR: Zinc for the common cold. Cochrane Database Syst Rev 6:CD001364, 2013. doi: 10.1002/14651858.CD001364.pub4

4. 4. Hemilä H: Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open 8(5):2054270417694291, 2017. doi:10.1177/2054270417694291

5. 5. Hunter J, Arentz S, Goldenberg J, et al. Zinc for the prevention or treatment of acute viral respiratory tract infections in adults: a rapid systematic review and meta-analysis of randomised controlled trials. BMJ Open 11(11):e047474, 2021. doi:10.1136/bmjopen-2020-047474

6. 6. Baqui AH, Zaman K, Persson LA, et al: Simultaneous weekly supplementation of iron and zinc is associated with lower morbidity due to diarrhea and acute lower respiratory infection in Bangladeshi infants. J Nutr 133(12):4150-4157, 2003. doi: 10.1093/jn/133.12.4150

7. 7. Lazzerini M, Wanzira H: Oral zinc for treating diarrhoea in children. Cochrane Database Syst Rev 12:CD005436, 2016. doi: 10.1002/14651858.CD005436.pub5

8. 8. Chew EY, Clemons TE, Agron E, et al: Long-term effects of vitamins C and E, beta-carotene, and zinc on age-related macular degeneration: AREDS report no. 35. [published correction appears in Ophthalmology 123(12 ):2634, 2016]. Ophthalmology 120(8):1604-11.e4, 2013. doi:10.1016/j.ophtha.2013.01.021

9. 9. The Age-Related Eye Disease Study 2 (AREDS2) Research Group, Chew EY, Clemons TE, et al: Secondary analyses of the effects of lutein/zeaxanthin on age-related macular degeneration progression: AREDS2 report No. 3. JAMA Ophthalmol 132(2):142-149, 2014. doi: 10.1001/jamaophthalmol.2013.7376

10. 10. Wang X, Wu W, Zheng W, et al: Zinc supplementation improves glycemic control for diabetes prevention and management: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr 110(1):76-90, 2019. doi: 10.1093/ajcn/nqz041

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

1. National Institutes of Health (NIH): Zinc fact sheet for health professionals